Method of making low carbon steel using ferrous oxide and mineral carbonates

ABSTRACT

A cored wire injection with a filling of iron oxide and mineral carbonate provides an improved method and apparatus for increasing and maintaining dissolved oxygen in the steelmaking process, while also providing a method for forming carbon dioxide for stirring and carbon oxidation in the molten steel bath. The method and apparatus are particularly useful for low carbon steel production by lowering the tap oxygen content in the furnace and preventing high amounts of iron oxide in the slag. Injecting a cored wire containing a mineral carbonate in the ladle after the furnace melting process provides sources of oxygen and a method of stirring the steel and reducing the partial pressure of CO needed to lower the carbon content.

RELATED APPLICATIONS

This application claims benefit and priority from U.S. provisionalapplication No. 61/631,423 accorded a filing date of Jan. 4, 2012.

FIELD OF INVENTION

This invention relates generally to a material and method for reducingthe carbon and alloy content in molten steel.

DESCRIPTION OF RELATED ART

Various steel making technologies have been developed since theBessemer/Kelly bottom blown furnace and the Siemens open hearth furnacebreakthroughs in the mid 19^(th) century. Open hearth steelmakingpredominated steel production through the mid 1960's. Electric arc andbasic oxygen furnaces have completely replaced Bessemer/Kelly processesand open hearth steelmaking in the USA and most of the world.

Molten steel is normally produced in an Electric Arc Furnace (EAF) usingprimarily solid ferrous scrap or other solid iron derivatives, or aBasic Oxygen Furnace (BOF) using hot molten iron containing up to 4.0% Cand scrap, or other solid iron derivatives. In the EAF, steel is meltedusing a combination of electrical and chemical energy. Melting of scrapin the BOF process is accomplished by chemical energy alone. In both theEAF and BOF process, the molten metal is refined using a flux to removesome of the sulfur and most of the phosphorous while providingprotection to the refractory lining. Oxygen is blown into the moltenmetal to remove carbon, phosphorous, aluminum, chrome and silicon fromthe molten bath through an oxidation process. The oxidation process isexothermic which emits heat and assists in taking the molten metal up tothe proper tapping temperature.

Once the molten metal is at the proper temperature and chemistry it istapped from the EAF or BOF into a refractory lined ladle. During tappingoperations, steel is poured out of the furnace vessel into a ladle. Atsome primary steel making shops the steel is tapped with between 50 to1500 ppm dissolved oxygen. During tapping operations the only additionto the ladle may be high carbon ferro manganese (Mn 75% minimum, Si 4.0%maximum, C 7.0 maximum, S 0.03% maximum and P 0.7% maximum). The ferromanganese is an alloying agent and a deoxidizer. The carbon, silicon andmanganese contained in ferro manganese all combine with the dissolvedoxygen in the molten steel. Carbon forms gaseous carbon monoxide.Silicon forms silica. Manganese forms manganous oxide. Not all of thecarbon forms carbon monoxide. A small amount of the carbon will alloywith the molten steel. Carbon levels may range up to 0.10% in the moltensteel in the ladle depending on the carbon level in the EAF just priorto tap and the total amount of ferro manganese added to the ladle.

During tapping in some melt shops, high carbon ferro manganese additionsmay be limited up to 0.20% of the total molten steel weight in the ladleif an artificial ladle slag is added. Artificial slags may containcalcium aluminate, calcia, doloma and calcium fluoride (spar). If noartificial slag is added the high carbon ferro manganese addition mayrange up to 0.60%.

In order to further lower the carbon in the ladle just after tap,steelmakers will stir the ladles with argon or nitrogen through a porousplug in the ladle or through a stirring lance to induce oxygen from airinto the steel. Stirring produces a roiling action on top of the moltenmetal bath. Bare molten metal is exposed to atmospheric air. Theaddition of dissolved oxygen from the air to the molten metal combineswith some of the carbon to form carbon monoxide. Sometimes a workmanwill point a hand oxygen lance at the bare metal roiling on top of theladle to enhance the formation of carbon monoxide in the molten steel.The gaseous carbon monoxide evolves out of the molten steel thusremoving carbon according to the following reactions:

Fe+½O₂=>FeO  1.

FeO+C=>Fe+CO  2.

and

C+½O₂=>CO  3.

As the dissolved oxygen content in the molten steel increases, thecarbon level drops in the molten steel. When the carbon level in themolten steel gets below 0.06%, dissolved oxygen in the steelexponentially increases resulting in the formation of large amount ofmolten iron oxide in the slag. As the dissolved oxygen content increasesin the molten steel, the iron oxide level in the slag can rapidlyincrease from 10% to 55%. Iron oxide increases in the slag represent ayield loss of iron available in the furnace for further processing.Yield from raw ferrous charge materials can drop from 1% to 5% dependingon the slag weight and iron oxide percentage in the slag. Additionally,iron oxide in the slag attacks furnace refractories causing erosion andpossible steel and slag leakage from the furnace shell.

Thermodynamically it is possible increase the dissolved oxygen contentfrom atmospheric air to remove carbon but the ladle must be violentlystirred with resulting damage due to liquid metal roiling against theladle refractory lining. Stirring gasses are induced to the ladle atrates up to 2 meters cubed per minute (70 cubic feet per minute).Stirring results in a violent roil in the slag layer on top of theladle. Severe erosion of the ladle refractory lining occurs in theregion of the roiling.

Vacuum degassing may also be used to lower carbon in a ladle containingmolten steel. Vacuum degassing is very useful for making steel with<0.025 carbon. Many carbon steel plants do not have vacuum degassersavailable. Vacuum degassers represent a large capital cost and anadditional processing step.

Another process used for steelmaking which produces a low carbon steelis known as the OBM or Q-BOP. This process involves injecting gaseousoxygen and hydrocarbons into the bottom of the refining vessel throughtuyeres. A very intense mixing is induced in the molten metal leading tocarbon levels as low as 0.015% without excess iron oxide production.

In liquid iron at 1873 K (1600° C.), thermodynamic equilibrium isdefined by the following equation:

([a _(c) ]=[a _(o) ]/Pco)=2.0×10⁻³

-   -   where a_(c) is the activity of carbon in % C, a_(o) is the        activity of dissolved oxygen in % O and Pco is the partial        pressure of carbon monoxide in atmospheres.

The equation clearly indicates that as the dissolved oxygen increases,the partial pressure of carbon monoxide must increase to maintainequilibrium thus resulting in the removal of carbon from the molteniron. When the sum of the partial pressures of all of the dissolvedgasses in the molten steel is greater than 1.0 atm, removal of carbonoccurs in the form of CO gas evolving out of the molten steel.

Chemical reheating is regularly used in the steel industry to providetemperature increases to molten steel. Chemical heating is performed byreacting a fuel and an oxidizer. Heat is emitted from the reaction.Dissolved oxygen in the molten metal and in oxides such as MnO and SiO₂serve as oxidizers. The primary fuels are Al or Si. The basic reactionsare either:

2Al+3/2O₂(dissolved)=>Al₂O₃

with 31,129 kJ/kg (13,383 BTU/lb) Al heat generated; or

Si+O₂(dissolved)=>SiO₂(solid)

With 33,857 kJ/kg (14,556 BTU/lb) Si heat generated.

Additional reactions to consider are:

2Al+Fe₂O₃=>Al₂O₃+2Fe

with 16,298 kJ/kg (7007 BTU/lb) Al heat generated; or

3Si+2Fe₂O₃=>3SiO₂+4Fe

with 14,798 kJ/kg (6362 BTU/lb) Si heat generated.

Both reactions are exothermic and generate heat in the molten steel.Furthermore, Ca, CaSi, and Mg can be used as fuels to increasetemperature in molten steel but at a higher energy cost per kJ ascompared to aluminum or silicon.

Prior to the widespread availability of bulk gaseous oxygen, ferrousoxide was added into the slag on top of steel melts to provide fordecarburization. Steelmakers would add mill scale, a common source offerrous oxide, to the top of the steel bath in the final refiningstages. The mill scale containing ferrous oxide would melt in the slag.At steelmaking temperatures, the mill scale would transfer oxygen to themolten steel at the slag-metal interface. The oxygen would then combinewith the carbon in the molten steel to form CO. The CO would out gasfrom the molten steel. CO formation from the carbon in the molten steeland the additional oxygen from mill scale would reduce the carboncontent in the steel. This method has largely been abandoned due to thefact that reduction of carbon by gaseous oxygen injection provides forfaster carbon reduction.

Additionally, it has been found that certain materials may be added tothe molten metal during the steel making process for various reasons.One method of introducing these desirable additives is the use of acored wire injection. Use of cored wire injection in the steel making isknown in the art. For example, Sarbendu et al, U.S. Pat. No. 7,682,418describes a cored wire injection process. It describes a method ofinjecting cored wire into the liquid steel bath. Cored wire allows forthe subsurface release of additives while controlling the zone ofrelease. The addition of additives can be controlled by changingdimensions of the cored wire and the speed of injection depending on theneeds of the steel making process. Cored wire commonly has an outercoating, usually a continuous steel tube, which is filled with variousadditives, including lead, sulfur, selenium, tellurium, and bismuth asfilling material. Cored wire containing calcium or mixture of calciumsilicon is normally injected to liquefy alumina inclusions andameliorate ladle and tundish nozzle clogging. A different type of coredwire method for treating molten metal is seen in King et al, U.S. Pat.No. 6,508,857. This is primarily an aluminum sheath forming a compositecore with a calcium inner core encased in a steel jacket. The WeinerU.S. Pat. No. 4,773,929 patent deals with a chemical method of reheatingmolten steel using solid metal as a fuel and an oxidizer contained in acored wire. Ferrous oxide is used in the mixture to provide a source ofoxygen for the chemical reaction. This reaction is more commonly knownas the thermite reaction and is very well known among chemists,metallurgists and welders. The Tiekink EP 1,715,065 uses a metal orcompound with a vapor pressure higher than the vapor pressure of calciumat steel making temperatures to provide a gas which will stir the moltensteel and provide for better distribution of calcium in the moltensteel. It's well known that metals such as zinc or magnesium or sodiumtransform to a gas at molten steel making temperatures. The addition ofsmall amounts of Zn or Mg or Na to a cored wire containing calcium canprovide an intense localized stirring action.

SUMMARY OF THE INVENTION

The current invention uses a cored wire injection with a filling of ironoxides and a mineral carbonate to provide an improved method andapparatus for increasing and maintaining dissolved oxygen in thesteelmaking process while also providing a method for forming carbondioxide for stirring and carbon oxidation in the molten steel bath. Thisinvention is particularly useful for low carbon steel production. Thisinvention allows for tapping electric arc or basic oxygen furnaces athigher levels of carbon thus lowering the tap oxygen content in thefurnace and preventing the high amounts of iron oxide in the slag whichin turn leads to iron yield improvements and cost savings. Injecting acored wire containing a mineral carbonate in the ladle after the furnacemelting process provides sources of oxygen and a method of stirring thesteel to lower the carbon content. Thus the dangerous and expensiveeffects of increasing dissolved oxygen in either the electric arc orbasic oxygen furnace can be eliminated.

The use of a cored wire injection with the iron oxides and mineralcarbonate filling reduces the risk to an operator in the steelmakingprocess who otherwise would be using a lance to stir the steel in theladle. Use of the cored wire reduces the risk of damage to the ladlerefractory lining. It provides more precise control of the process forthe operator while reducing costs. Injecting a cored wire containingferrous oxide and a mineral carbonate is useful for making low carbonsteel grades with 0.015 to 0.06% carbon as opposed to the currentmethods of blowing oxygen into the furnace or using a vacuum degasser.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cored wire showing filling material and raised seam prior toseam being bent flush.

FIG. 2 is the cored wire showing particulate material and with the seambent flush along the circumference of cored wire.

FIG. 3 is the particulate material on steel strip prior to being formedinto a tube.

FIG. 4 shows the cored wire feeding into a ladle containing moltensteel.

DESCRIPTION OF THE INVENTION

FIG. 1 shows the cored wire (100) consists of a filling (200) made ofparticular material and a metal jacket (110) made out of steel. Themetal jacket (110) is usually made from a soft mild carbon steel rangingfrom 0.4 to 0.5 mm thick. The metal jacket (110) provides the followingfunctions:

1. Contains the filling (200);2. Keeps the filling (200) dry;3. Prevents the filling (200) from reacting in the liquid slag layer ontop of the ladle; and4. Provides rigidity for the filling (200) to penetrate into the moltensteel.

The cored wire (100) is preferably wound into a coil (400) and placed ona reel. The metal jacket (110) starts as a flat ribbon like constructionand is formed into the cylinder that holds the filling (200). The flatribbon like material is bent into a cylinder with the seam (120) holdingthe filling (200) in place inside the cored wire (100).

FIG. 2 shows the cored wire (100) with the seam (120) bent flush withthe circumference of the cored wire (100). The filling (200) is composedof oxides of iron containing FeO, Wustite, Fe₂O₃, Hematite, Fe₃O₄,Magnetite, and mineral carbonates such as CaCO₃, MgCO₃ or CaMg(CO₃)₂.One source of oxides of iron is mill scale. Mineral carbonates can besourced from calcium carbonate, magnesium carbonate or calcium magnesiumcarbonate. The filling (200) fills substantially the entire interstitialspace available inside the cored wire.

FIG. 3 shows the filling (200) on a ribbon like portion of the metaljacket (110) before the metal jacket (110) is formed into the cored wire(100) as shown in FIGS. 1 and 2. The ribbon like metal jacket (110) willthen be formed into the cored wire (100) around the filling (200) andsealed with a seam (120) at the top. The seam (120) will be bent overflat onto the

circumference of the cored wire (100). The cored wire (100) will then bewound into a coil (400) with the weight of the coil ranging from 113.4kg to 2.268 kg (250 to 5000 lb).

FIG. 4 shows the cored wire (100) feeding into a ladle (500) containingmolten steel (600). A cored wire-feeding machine (550) is normally usedto feed the wire (100) into a ladle. One end of the cored wire (100) isplaced over the top of the ladle (500). The wire-feeding machine (550)is started and the cored wire (100) is advanced through the top layer ofslag into the liquid steel (600) contained in the ladle (500).

The metal jacket (110) forming the outer shell of the cored wire (100)prevents premature melting of the filling (200) so reactions can takeplace in the molten steel (600) and not in the slag layer. The feedingspeed can be varied to allow melting of cored wire (100) at variousdepths in the ladle (500).

Using the above described cored wire injection process a cored wire(100) is injected into the ladle (500) containing the molten steel. Thecored wire includes a metal jacket (110), and a filling (200) thatcontains oxides of iron and a mineral carbonate. Oxides of iron are usedto provide oxygen to the steel in the ladle. Mineral carbonates are usedto form CO₂ for stirring and further carbon oxidation in the moltensteel bath.

Three reactions may occur depending on the type of mineral carbonateused:

CaCO₃=>CaO+CO₂  1.

MgCO₃=>MgO+CO₂  2.

CaMg(CO₃)₂=>CaO+MgO+2CO₂.  3.

In a non-deoxided steel such as being treated in this application theCO₂ undergoes a further reaction to help decarburize the steel:CO₂+C=>2CO.

Additionally two secondary reaction occurs with the CO₂ to further helpdecarburize the steel:

CO₂+Fe=>CO+FeO  1.

FeO+C=>Fe+CO.  2.

The formation of CO₂ in the ladle provides a mechanism to promoteintense localized sub-surface mixing kinetics in the ladle.

In a synergistic effect, the use of CO₂ as a stirring agent helps tolower the partial pressure of CO needed for carbon oxidation.

The following table indicates the maximum volume of CO₂ gas generated atstandard temperature and pressure conditions (STP):

Maximum CO₂ Production Rate Injection Material CaCO₃ MgCO₃ CaMg(CO₃)₂CO₂ production CO₂ production CO₂ production Mineral Carbonate rate raterate Injection Rate Nm³/hr Nm³/hr Nm³/hr kg/min (lb/min) (scfm) (scfm)(scfm) 0.454 (1)  6.80 (4)  6.80 (4)  6.80 (4)  0.908 (2)  11.9 (7) 15.3 (9)  13.6 (8)  1.36 (3)  18.7 (11) 22.1 (13) 20.4 (12) 2.27 (5) 30.6 (18) 35.7 (21) 32.3 (19) 4.54 (10) 61.2 (36) 73.1 (43) 66.3 (39)6.81 (15) 91.8 (54)  108 (64) 98.6 (58) 9.08 (20)  122 (72)  144 (85) 133 (78) 13.6 (30)   184 (108)   218 (128)   199 (117) 18.1 (40)   245(144)   289 (170)   265 (156) 22.7 (50)   306 (180)   362 (213)   331(195)

The CO₂ production rate is controlled by the injection speed and weightof mineral carbonate contained in a given length of cored wire. Thecored wire has various oxides of iron that have varying amounts ofoxygen as a by weight percentage. This percentage ordinarily variesbetween 10% and 30%. The use of the cored wire (100) contains a filling(200) that comprises in part various forms of oxides of iron containingwustite, hematite, and/or magnetite, and allows a precise method andapparatus for increasing and maintaining dissolved oxygen somewherebetween 1 and 1800 parts per million in a ladle of molten steel.Ordinarily the amount of oxygen to the ladle of steel may vary from 1part per million and 1800 parts per million. A simple calculation basedon the filling (200) and the cored wire (100) an injection rate allowsan operator to control the amount of oxygen added. In industrialapplications the actual range added will usually fall between a low of0.00333 kilograms of oxides of iron per metric ton added to a high of 18kilograms per metric ton of molten steel of oxides of iron added usingthe cored wire (100). The amount of mineral carbonates on a weight basismixed in with the ferrous oxide will vary from 1 to 90%. The finalpercentages of a ferrous oxide and mineral carbonate mixture used at aparticular operation will depend on cored wire injection velocity, coredwire diameter, and the desired outcome. It should be noted that if thepercentage of mineral carbonate is too high and the injection speed istoo high, violent stirring will take place in the ladle and steel willsplash out of the ladle. Thus, a lower percentage of mineral carbonateswill be needed for high injection rates. A case may be made for veryslow injection speeds which will allow for more reaction times. In thissituation a higher percentage of mineral carbonate will be needed in thecored wire to provide adequate CO₂ gas generation rates.

Combining ferrous oxide and a mineral carbonate in the same cored wireprovides a synergistic effect for removing carbon. As the mineralcarbonates degrade into a mineral oxide and gaseous CO₂, an intenselocalized stirring action occurs deep inside the ladle of molten steel.Kinetic action stirs the ferrous oxide into solution and forces fasterformation of CO which removes the carbon from the molten steel. With theintense stirring and the lowering of the partial pressure of CO gasneeded for carbon removal by CO₂ generation from the mineral carbonate,minimum carbon levels of 0.015% can be realized as opposed to 0.025% Cachieved with normal oxygen blowing methods. Additionally, some of theCO₂ will react further with the molten steel's carbon to help formsupplementary CO gas for accelerated carbon removal. The addition of amineral carbonate greatly assists carbon removal as opposed to injectingonly a ferrous oxide material. Injecting a cored wire containing ferrousoxide and mineral carbonates provides a novel and unobvious method fordecarburization by providing an oxygen source, stirring the moltenmetal, and lowering the partial pressure of CO needed for carbonremoval. The total pressure of gasses required for carbon removal frommolten steel must exceed 1 atm:

P_(CO)+P_(N2)+PAr+P_(CO2)>1 atm. As the partial pressures of Ar, N₂ andCO₂ are increased, the partial pressure of CO needed to remove C isreduced. The CO₂ obtained from the calcium carbonate will produce verysmall gas bubbles thus increasing the surface area for reactions. Theuse of nitrogen is discouraged in low carbon steelmaking since it canproduce unwanted physical properties when the steel solidifies. Highvolumes of argon gas injected into a ladle through a lance or porousplug tends to coalesce and form very large bubbles thus reducing theamount of surface area for reactions.

Mineral carbonates have been added to steelmaking slag as a foaming andrefining agent. As the mineral carbonate breaks down, carbon dioxide isevolved in gaseous form. Some of the carbon dioxide will further degradeinto CO and O₂. Additionally, any remaining metallic P, Cr, B, Ti, Si,Al, Ca, and Mg will be oxidized into inclusions of P₂O₅, Cr₂O₃, B₂O₃,TiO₂, SiO₂, Al₂O₃, CaO and MgO. The inclusions will float to the top ofthe bath and be trapped in the slag layer.

The slag rises due to the gas evolution much like foam on a glass ofbeer. This invention injects the mixture of mineral carbonates below thesurface of the molten metal so all of the contained liquid is mixed, notjust the slag. This provides momentum to the molten metal and causesintense localized mixing. Rather than relying on additional stirringaction from a porous plug or ladle lance, the injected cored wireprovides its own agents for stirring the molten metal.

The following method may be used for increasing the dissolved oxygencontent in a ladle of steel:

1. The molten metal contained in the melting furnace is at the desiredtemperature and chemistry. A steelmaker normally tests the molten steelusing a thermocouple, oxygen probe and sampler. The sampler sucks up asmall quantity of molten metal where it is instantly solidified into ashape suitable for optical emission spectrographic (OES) testing. Theoxygen probe provides the level of dissolve oxygen in the molten metalin the bath. If the temperature, oxygen level and chemistry are withinspecification, the furnace is ready to be drained in an operation knownas tapping.2. The furnace is opened and molten metal is tapped into a ladle. Thefurnace is primarily a melting vessel. Further refinement of the moltensteel takes place in a refractory lined ladle. This step also frees upthe furnace to melt the next order of steel. Tapping operations normallytake from 3 to 12 minutes. Tapping is a very spectacular operation withhot glowing molten metal flowing through the air from the furnace intothe ladle. The flow rate out of the furnace is normally controlled by anoperator continuously adjusting the tilt angle.3. During tapping, ferro-manganese may or may not be added to the ladle.No other ferro alloys are added during tapping operations for thisinvention. The addition of ferro alloys is restricted to allow for theachievement of high dissolved oxygen levels, >100 ppm, in the ladle posttap. In some operations aluminum, silicon or silico-manganese are addedduring tap to decrease dissolved oxygen in the molten metal. The intentof this invention is to keep the dissolved oxygen levels at a >100 ppmlevel so that the removal of carbon is easier.4. Fluxes such as calcium aluminate, calcia, doloma or calcium fluoride(spar) are added to the ladle during tapping operations. Fluxes are usedprimarily for the removal of sulfur and protection of the ladle duringrefinement operations. Fluxes also help to reduce the activity ofdissolved oxygen in the molten metal so if an operator wishes a higherdissolved oxygen level for carbon oxidation from the molten steel, theamount of fluxes added during tapping operations will be reduced ascompared to normal levels.5. Cored wire containing various forms of oxides of iron containingwustite, hematite or magnetite and a mineral carbonate are injected intothe ladle during tapping operations. Tapping operations alone generate aroil in the ladle to promote mixing. Simultaneously, argon or nitrogenis injected into the ladle either through a lance or porous plug to aidin the agitation of the molten metal. The agitation is furtherintensified by the evolution of carbon dioxide gas from the cored wireaddition. The intense kinetic energy imparted by stirring promotes themixing of ferrous oxides with the dissolved carbon in the melt. Anintense but controlled stir from the tapping operation, argon ornitrogen gas injection and carbon dioxide evolution from the mineralcarbonate addition in the cored wire accelerates the reaction time. Thisis unique.

Alternatively, the ferrous oxide plus mineral carbonate cored wire maybe injected after tapping is completed. This step can be conductedbehind the melting furnace, at an intermediate station or at a ladlerefining operation. The kinetic energy from the molten metal flowingfrom the furnace into the ladle is lost but in some operations it may bemore practical to inject the cored wire later in the process. The ladlewould be stirred with nitrogen or argon through a lance or porous plugwhile addition stirring energy would be imparted from the evolution ofcarbon dioxide gas splitting off from the mineral carbonates. This isalso unique.

6. The dissolved oxygen content in the molten metal is increased by oneto 1800 ppm by the injection into the ladle of cored wire containingvarious forms of oxides of iron containing wustite, hematite and ormagnetite and a mineral carbonate. It is desirable that the dissolvedoxygen content in the molten metal is increased by one to 1800 ppm bythe injection into the ladle of cored wire, with the process conditionsdictating the amount of oxygen increase needed for carbon removal. Theinjection speed will range from 10 feet per minute up to 1500 feet perminute.

Carbon removal is accomplished by increasing the oxygen content in themolten metal. A simple reaction of C+O═CO provides the essentialdescription of carbon removal from molten steel. As the dissolved oxygencontent increases, the level of retained carbon decreases. Both ferrousoxide and carbon dioxide provide oxygen to the process for carbonoxidation and removal. Some additional oxygen for carbon reduction maybe provided from the air atmosphere directly above the ladle.

In general, the higher the dissolved oxygen content, the lower the levelof retained carbon in the molten metal. Optimizing this is unique.

7. P, Cr, B, Ti, Si, Al, Ca and Mg alloyed with the molten steel will beoxidized prior to C affecting their removal from the molten steel bath.8. After the dissolved oxygen content is increased and the carbon is atthe desired level, additions of cored wire rod form or alloy lump ofaluminum, silicon, ferro-silicon, silico-manganese, calcium-silicon,calcium metal, or magnesium may be added to the molten metal in theladle. An addition of any of the above mentioned materials causes anexothermic reaction thus raising the temperature of the molten metal.The dissolved oxygen level is reduced and the molten metal is ready forfurther refinement.9. The ladle of molten metal is then taken to the ladle furnace or othermetallurgical refinement process, such as a vacuum degasser, for finaltreatment into a castable, sellable material. Most steel produced nowuses a secondary refining station. Use of secondary refining stationshas led to productivity and quality improvements.10. Alternatively, as mentioned in Step 5, after tapping is complete andthe ladle is at a secondary refining station, injection of cored wirecontaining various forms of oxides of iron containing wustite, hematiteand or magnetite and a mineral carbonate are injected into the ladle atthe start of secondary refining operations prior to the addition of anyferro alloys or carbon. No other alloys other than ferro manganese havebeen added up to this point.

Due to the physical layout of many steel melt shops, injection of coredwire may be more easily accomplished at the secondary refining unitrather than just after tapping.

11. Alternatively, at the secondary refining station, after the coredwire containing various forms of oxides of iron containing wustite,hematite and or magnetite and a mineral carbonate are injected into aladle, additional alloying operations may be accomplished after thecarbon is at the desired level as detailed in Step 7. Additional fluxesmay be added to the ladle of steel for sulfur removal during and afterthe alloying operations. The addition of ferrous oxides containingmineral carbonates, most ferro alloys and fluxes tend to reducetemperature in the molten metal. At a ladle furnace, the molten metalcan be reheated to the desired temperature. The use of a ladle furnacestation for carbon removal using a cored wire containing ferrous oxideand mineral carbonates is a desirable alternative to injection behindthe furnace or at an intermediate station. This is unique.

Specific Advantages to the Process

Injecting oxygen using a lance into a ladle or stirring the molten metalin the air is a slow process as compared to increasing oxygen using acored wire containing ferrous oxide. When comparing the oxygen injectionrate between a lance running at 2.12 normal cubic meters per minute (75scfm) and a 13 mm diameter cored wire containing ferrous oxide, theoxygen injection rate using the cored wire is 7 times faster. Operatorscould tap an EAF at a lower oxygen level which will lead to fasterproduction times, less refractory wear and lower yield losses.

Lowering carbon in a ladle using a cored wire containing ferrous oxidesand mineral carbonates provides an inexpensive method for loweringcarbon outside of the melting furnace. Current methods for post meltingcarbon reduction involve using a vacuum degasser at a large capitalcost. Any steel melt shop could readily acquire and install a wirefeeder needed for this process at 1/10 to 1/20^(th) of the cost of avacuum degasser and start making low carbon steel in the ladle. Steelcould be tapped from the melting furnace at higher carbon levels leadinghigher productivity and yields from raw materials.

It should be understood, of course, that the foregoing relates toexemplary embodiments of the invention and that modifications may bemade without departing from the spirit and scope of the invention as setforth in the following claims. In addition, the same method could beapplied to achieve other stoichiometric goals. By way of example, if thealloy level is too high in a ladle of steel the injection of ferrousoxide will help to readily oxidize excessive alloys such as P, Cr, B,Ti, Si, Al, Ca and Mg and remove the materials in oxide form to the slaglayer on top of the ladle. It should also be understood that ranges ofvalues set forth inherently include those values, as well as allincrements between. For example, 1-5 includes 1; 1.1; 1.2 and so forthuntil 5. It should also be understood that, as used herein,“approximately” and the like are +/−5%, and “substantially” means to theextent reasonably possible when considering human and machinevariations. Also, it should be understood that these processes can takeplace in an industrial ladle having a capacity of approximately 10 tonsto approximately 400 tons of molten metal.

What is claimed is:
 1. An improved method of making low carbon steeltapped from an Electric Arc Furnace or a Basic Oxygen Furnacecomprising: A. Providing a cored wire injection apparatus with coredwire containing a filling of at least a mixture of iron oxides andmineral carbonates; and B. injecting said cored wire into a ladle ofmolten steel of an approximate known mass, said in at a predeterminedrate; whereby O₂ from said iron oxides is distributed in said moltensteel in part by release of CO₂ from said mineral carbonates therebyreducing carbon in said molten steel to a desired level and said releaseof CO₂ increases total pressure of gasses in said molten metal andreduces partial pressure of CO needed to remove C from said moltenmetal. 2) An improved method of making low carbon steel tapped from anElectric Arc Furnace or a Basic Oxygen Furnace of claim 1 furthercomprising: establishing that said filing has a predetermined percentageof iron oxides and a predetermined percentage of mineral carbonates sothat a mass of iron oxide and a mass of mineral carbonates is definedfor a particular length of cored wire. 3) An improved method of makinglow carbon steel tapped from an Electric Arc Furnace or a Basic OxygenFurnace of claim 2 further comprising a step of calculating saidpredetermined rate of injection of said cored wire so that apredetermined mass of iron oxide and mineral carbonate is added to saidapproximate known mass of molten steel to insure said distribution of O₂into said steel by said CO₂ is effective for removing carbon from saidknown mass of molten steel. 4) An improved method of making low carbonsteel tapped from an Electric Arc Furnace or a Basic Oxygen Furnace ofclaim 3 wherein said step of calculating a rate of injection results ina slower rate of injection when said percentage of mass of mineralcarbonates per particular length of cored wire is higher whereby a rateof mixing of said molten steel by release of CO₂ from said mineralcarbonates is controlled. 5) An improved method of making low carbonsteel tapped from an Electric Arc Furnace or a Basic Oxygen Furnace ofclaim 4 wherein said cored wire is added to said know mass of moltenmetal to provide O₂ so that said added O₂ is in a range between 1 ppmand 1800 ppm. 6) An improved method of making low carbon steel tappedfrom an Electric Arc Furnace or a Basic Oxygen Furnace of claim 5comprising additional steps of determining said molten metal has betweenapproximately 0.015% and approximately 0.03% by weight of dissolvedcarbon then creating an exothermic reaction in said molten metal therebyreducing dissolved O₂ in said molten metal. 7) An improved method ofmaking low carbon steel tapped from an Electric Arc Furnace or a BasicOxygen Furnace of claim 6 wherein said added O₂ is in a range of 500 ppmto 1200 ppm. 8) An improved method of making low carbon steel tappedfrom an Electric Arc Furnace or a Basic Oxygen Furnace of claim 7wherein said cored wire is added during tapping. 9) An improved methodof making low carbon steel tapped from an Electric Arc Furnace or aBasic Oxygen Furnace of claim 7 wherein said cored wire is added aftertapping. 10) A method of decreasing dissolved oxygen in molten steelincluding the steps of: A. Opening a furnace and tapping molten metalinto a ladle; B. Adding fluxes into the ladle during tapping; C.Injecting cored wire into the ladle at an inject speed ranging fromapproximately 10 feet per minute to approximately 1500 feet per minute,said cored wire including components selected from ferrous oxide,mineral carbonate and combinations thereof; and D. Ceasing the coredwire injection when normalized dissolved carbon is between approximately0.015% and approximately 0.0.05% by weight. 11) The method of claim 10further including the step of adding ferro-manganese while tappingmolten metal into the ladle in an amount sufficient to achieve >100 ppmoxygen in the ladle after tapping. 12) The method of claim 10 whereinthe step of adding fluxes into the ladle during tapping includes addingfluxes selected from calcium aluminate, calcia, dolma, calcium fluorideand combinations thereof. 13) The method of claim 10 wherein the step ofinjecting cored wire is performed during tapping. 14) the method ofclaim 10 wherein the step of ceasing the cored wire injection isperformed when normalized dissolved carbon is between approximately0.055% and approximately 0.015% by weight. 15) A method of lowering thepartial pressure of CO in the steelmaking process including the stepsof: A. Opening a furnace and tapping molten metal into a ladle, saidladle having a capacity of approximately 10 tons to approximately 400tons of molten metal; B. Injecting cored wire into the ladle in anamount sufficient to increase dissolved oxygen content of molten metalby approximately 1 ppm to approximately 1800 ppm; C. Confirming moltenmetal has between approximately 0.015% and approximately 0.055% byweight of dissolved carbon; and D. Creating an exothermic reaction toreduce dissolved oxygen level of molten metal. 16) method of claim 15wherein the step of injecting cored wire into ladle includes step ofinjecting in amount sufficient to increase dissolved oxygen content ofmolten metal by approximately 100 ppm to approximately 1200 ppm. 17)method of claim 15 further including the step of adding additionaloxygen to ladle by adding air from environment. 18) method of claim 15wherein the step of creating an exothermic reaction includes the step ofadding a component selected from aluminum, silicon, ferro-silicon,silico-manganese, calcium-silicon, calcium metal, magnesium orcombinations thereof. 19) method of claim 15 further including the stepof introducing the ladle of molten metal to a secondary refinementstation selected from ladle furnace, vacuum degasser or combinationthereof.